1. Field of the Invention
The present invention relates to epoxy resin compositions which are suitable for the formation of insulating layers for multi-layered printed boards.
2. Discussion of the Background
In recent years, a tendency of making electronic instruments small in size and highly efficient is increasing and, in a multi-layered printed board, a build-up layer is made into multi-layered, and a tendency of making the wiring finer and more dense is also further increasing. With regard to a method for the formation of a conductor layer suitable for the formation of fine wiring of high density, there have been known an additive method in which the surface of an insulating layer is subjected to a roughening treatment and then a conductor layer is formed by nonelectrolytic plating and a semi-additive method in which a conductor layer is formed by nonelectrolytic plating and electrolytic plating. In those methods, the adhesiveness of the insulating layer to a plated conductor layer (plated copper) is mostly ensured by means of the unevenness of the surface of an insulating layer (resin surface) formed by a roughening treatment (or, in other words, an anchor effect is achieved between the insulating layer and the plated layer because the surface of the insulating layer (resin surface) has unevenness). Accordingly, in enhancing the adhesiveness, there will be a way to make the degree of unevenness (roughness) of the surface of the insulating layer bigger.
However, for making the density of wiring higher, it is preferred that the roughness of the insulating layer surface (resin surface) is small. Thus, when the roughness of the insulating layer surface (resin surface) is high in case the wiring formation is finished by removal of a plated layer in thin membrane by means of flash etching after formation of a conductor layer (plated layer) by nonelectrolytic plating or electrolytic plating.
If the roughness of the insulating layer surface (resin surface) is large, a flash etching for a long time is necessary for removal of plated residue (smear) which gets into the concave when the wiring formation is finished by removal of a plated layer in thin membrane by means of flash etching after formation of a conductor layer (plated layer) by nonelectrolytic plating or electrolytic plating. On the other hand, if a flash etching is carried out for long time, in consequence of that, a risk of damaging or cutting fine wiring becomes high. Accordingly, in order to form a highly reliable wiring in a high density, it is demanded for the insulating layer surface that adhesiveness to a plated conductor is good, even when roughness after the roughening treatment is small. However, up to now, no insulating material which is able to form a rough surface having such a property has been developed.
JP-A-2005-154727 discloses that, when an epoxy resin composition containing specific two kinds of epoxy resins, a phenol type curing agent, a specific thermoplastic resin (such as polyvinyl acetal and phenoxy resin), and an inorganic filler in a predetermined rate is used in an insulating layer for a multi-layered printed board, it shows a low thermal expansion coefficient and is good in a peel strength of the conductor layer formed by a plating.
JP-A-2003-286390 discloses that, when an epoxy resin composition containing specific amounts of epoxy resin, multivalent hydroxy resin curing agent, phenoxy resin of a bisphenol A type or F type, specific rubber component, and curing promoter is used for an insulating layer, etc. of a multi-layered printed board, it shows good heat resistance, mechanical strength, film supporting property, etc.
JP-A-2004-286391 discloses that, when an epoxy resin composition containing specific amounts of epoxy resin, specific phenol vinyl aralkyl type resin curing agent, specific phenoxy resin, specific rubber component, and curing promoter is used for an insulating layer, etc. of a multi-layered printed board, it shows good heat resistance, mechanical strength, film supporting property, etc.
However, even in those Patent Documents which disclose various kinds of resin compositions as such, there is no disclosure of a resin composition which gives a low roughness and high peel strength for using as an insulating layer and there is no indication therein for such a problem to be solved.